The present invention deals with a turn signal in a vehicle. More particularly, the present invention deals with a monitor circuit for monitoring a turn signal in a vehicle.
Turn signals are commonly found on many different types of vehicles. For example, turn signals are found on motorcycles and in automobiles. Typical turn signals are activated when an operator wishes to signal a turn and manually throws a switch to activate a turn signal indicator. The switch closes a circuit to supply power to a flasher. The flasher has an internal bi-metallic contact which heats up when power is supplied to it. As the bi-metallic contact heats, it deforms or bends due to a difference in the coefficient of linear expansion in the two bi-metallic components of the flasher. As the bi-metallic contact bends, it opens a circuit which supplies power to a turn signal lamp mounted on the vehicle. When the circuit is broken, the lamp is extinguished.
When the bi-metallic contact bends and breaks the circuit, current is no longer flowing through the contact. Therefore, it begins to cool. As the bi-metallic contact cools, it resumes its original position closing the circuit to the turn signal lamp. This reestablishes the application of power to the turn signal lamp and the turn signal lamp is again illuminated. This cycle repeats itself causing the turn signal lamp to blink as is commonly known.
The turn signal which was initiated by the operator can be turned off either manually or automatically. The turn signal is turned off manually when the operator replaces the turn signal switch to its neutral position. The turn signal is turned off automatically, in an automobile, when the steering wheel is rotated a certain number of degrees and then rotated back to its nominal position.
However, certain undesirable conditions, and potentially hazardous conditions, result from the typical operation of a turn signal. For instance, during both city and freeway driving, vehicle operators are required by law in many states to signal lane changes using the vehicle's turn signal. The relative lateral movement of the vehicle to make a lane changer however, does not require the operator to rotate the steering wheel the minimum number of degrees to deactivate the turn signal. Therefore, the turn signal is not automatically turned off. Further, the operator may not notice that the turn signal is still activated. This gives other drivers on the freeway the false indication that the vehicle operator is signaling a lane change or a turn when, in fact, the operator does not intend to make such a change. This can potentially be hazardous.
The turn signal can also remain activated, without the operator's knowledge, under other circumstances. For instance, where a signaled turn is not a lane change, but rather a gradual turn which is commonly made to enter a freeway by an on ramp or to exit a freeway through an off ramp, such a turn often does not automatically disengage the turn signal. This can result in the turn signal remaining active without the operator knowing that it is active. Similarly, where a road branches and the operator signals to indicate that the vehicle will be taking either the right or left branch, the turn can be so gradual that it does not require the necessary steering wheel rotation to disengage the turn signal.
In all of these instances, an undesirable, and possibly hazardous, condition results. The turn signal on the vehicle is active, thus signaling to other vehicles an intended turn, when in reality the operator of the vehicle does not intend to make such a turn.
There have been several attempts to deal with the present problem. In one attempt, an alarm is provided to the operator when the turn signal is activated. The alarm simply continues until the turn signal is deactivated, either manually or automatically. However, this type of system presents certain problems. For example, the operator can very typically wait in line in a turn lane at a controlled intersection where the vehicles turn signal must remain on for (perhaps in heavy traffic) several minutes. In that instance, the alarm is provided continuously for the entire duration that the turn signal is on, until the operator reaches the intersection and actually makes the desired turn. This continuous alarm can become very annoying to the operator.
A similar disadvantage manifests itself during city driving, where there are many stoplights. An operator may spend a good portion of time at stoplights with a turn signal activated. Each time the turn signal is activated, the alarm is continuously presented to the operator. Such annoyances can not only be irritating to the driver, but can be distracting in the operation of the vehicle. The operator may simply tend not to signal every turn to avoid initiation of the alarm. This can be hazardous.
There have also been other attempts to deal with the problem of having the turn signal remain activated without the operator's knowledge. Such attempts have included automatic deactivation or termination of the turn signal after a predetermined time period. Also, prior systems have cancelled the turn signal when the speed of the vehicle has exceeded a predetermined threshold. Both of these prior attempts to solve the present problem are flawed from a safety standpoint. Both of these systems automatically disable the turn signal. They take the operator out of the loop so that it is no longer the operator's decision to deactivate the turn signal. Rather, the turn signal is deactivated automatically. Such a situation can result in the turn signal being terminated when the operator does not desire termination of the turn signal. This can result in the vehicle changing lanes without signaling, or making an unsignaled turn at an intersection. Such acts are as hazardous, if not more so, than having the vehicle signaling a turn when no turn is intended by the operator.